The present invention relates to a seat belt retractor installed in a vehicle such as an automobile for winding a seat belt onto a spool by a motor to restrain and protect an occupant and, more particularly, to a seat belt retractor for winding a seat belt efficiently by a motor using limited power. The present invention also relates to a seat belt device provided with the seat belt retractor.
Conventionally, a seat belt device installed in a vehicle such as an automobile prevents an occupant from jumping out of a vehicle seat by restraining the occupant with a seat belt thereof, thereby protecting the occupant in the event of emergency such as a vehicle collision at which large deceleration is exerted on the vehicle.
The seat belt device is provided with a seat belt retractor for winding up the seat belt. The seat belt retractor comprises urging means such as a spiral spring for urging a spool with the seat belt wound thereon in a belt-winding direction. When the seat belt is not used, the seat belt is fully wound on the spool by the urging force of the urging means. When the occupant puts on the seat belt, the seat belt is withdrawn against the urging force of the urging means to extend across the occupant. In the seat belt retractor, a locking mechanism is activated in the event of emergency as mentioned above to stop the rotation of the spool in an unwinding direction, thereby preventing the seat belt from being withdrawn. Therefore, the seat belt can securely restrain and protect the occupant.
As a conventional seat belt device as mentioned above, a motorized seat belt retractor has been proposed in which, when an unavoidable collision is detected before a vehicle collision, the tension on the seat belt is increased by increasing the driving force of the motor to wind up the seat belt, thereby increasing the restraint force of the occupant. When the vehicle collision is actually detected, a gas generator for a pretensioner is actuated to generate gas, so that the seat belt is rapidly wound up with the generated gas, thereby further increasing the restraint force of the occupant (see Japanese Patent Publication (Kokai) No. 2000-95064).
Japanese Patent Publication (Kokai) No. 2000-177535 has disclosed a seat belt retractor in which the belt tension is controlled. The seat belt retractor is provided with power transmission passages for transmitting the rotational torque of the motor, i.e. a first power transmission passage for transmitting the rotational torque of the motor to urging means to increase the force of the urging means and a second power transmission passage for transmitting the rotational torque of the motor at a fixed reduction ratio. The first power transmission passage is selected when a first solenoid is actuated, and the second power transmission passage is selected when a second solenoid is actuated.
It is necessary to wind up the seat belt with various modes such as a mode for rapidly winding up the seat belt for removing a slack of the seat belt or storing the seat belt and a mode for winding up the seat belt with large rotational torque for restraining the occupant. The rotational speed of the spool and the belt winding torque on the spool depend on the mode of winding up the seat belt.
In the seat belt retractor disclosed in Japanese Patent Publication (Kokai) No. 2000-95064, the power transmission mechanism transmitting the driving force of the motor to the spool has only one power transmission passage with a fixed reduction ratio. Accordingly, the reduction ratio is limited so that it is difficult to flexibly and effectively obtain various rotational speeds of the spool and various belt winding torques on the spool.
It is possible to control the rotational speed of the motor and the winding-up force of the spool through a fine control system. However, it is difficult to control the motor through such a fine control system, and the power consumption increases. It is necessary to increase the rotational torque of the motor in order to obtain large restraining force in the event of emergency such as a vehicle collision. However, when the rotational torque of the motor increases, the power consumption increases or a size of the motor increases.
In the seat belt retractor disclosed in Japanese Patent Publication (Kokai) No. 2000-177535, one power transmission passage is provided for transmitting the rotational torque of the motor to the urging means to control the urging force of the urging means, while the other transmission passage is provided for transmitting the rotational torque of the motor to the spool to directly control the winding-up force of the spool with the rotational torque of the motor. While the seat belt retractor is provided with the two different power transmission passages with the different speed reduction ratios, only one power transmission passage with a fixed reduction ratio is provided for directly transmitting the rotational torque of the motor to the spool. Accordingly, similarly to the device disclosed in Japanese Patent Publication (Kokai) No. 2000-95064, the reduction ratio is limited so that it is difficult to flexibly and effectively obtain various rotational speeds of the spool and various belt winding torques on the spool.
In the seat belt retractor, it is possible to control the belt winding force to some extent through the control of the urging force of the urging means with the rotational torque of the motor so as to control the belt winding force of the spool according to the controlled urging force. However, it is preferable to control the winding force of the spool more accurately by effectively utilizing the rotational torque of the motor.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide a seat belt retractor with a compact structure in which power consumption of a motor is reduced and control of the motor is simple, wherein the seat belt retractor effectively achieves two winding modes, i.e. a mode for rapidly winding up the seat belt for removing slack of the seat belt or for storing the seat belt, and a mode for winding up the seat belt with large winding force for restraining the occupant. Another object of the present invention is to provide a seat belt device provided with the seat belt retractor.
Further objects and advantages of the invention will be apparent from the following description of the invention.